In recent years, global warming becomes a severe problem, and hence a demand for saving the energy of electrical appliances increases. Since nowadays about 55% of a domestic annual energy consumption amount is consumed by motors, the concern for increasing the efficiency of the motor is high. In order to improve the efficiency of the motor, a design of using a rare earth magnet having a high energy product has been employed so far.
However, Nd (Neodymium) or Dy (Dysprosium) as a material of the rare earth magnet recently rises in price due to the export ceiling regulation of China as the greatest production country. The policy of the export ceiling regulation of China is determined to prevent the environmental destruction caused by the mining of Nd or Dy. Thus, there is a high possibility that the rare earth material rises in price or the supply shortage thereof occurs even in the future.
For this reason, as a method of improving the efficiency of the motor only by a ferrite magnet without using the rare earth magnet, an axial gap motor has gained attention. Since the axial gap motor can obtain a wide magnet area compared with an existing radial gap motor, it is possible to compensate a decrease in holding force when the ferrite magnet is selected and hence to obtain the efficiency equal to or more than in the related art.
As the configuration of the axial gap motor, a combination such as a one-rotor/two-stator type, a two-rotor/one-stator type, and a one-rotor/one-stator type is known.
Patent Document 1 below discloses an axial gap motor (one rotor/one stator type) by continuously winding four same phase coils and connecting by the Y-connection. Here, since the number of connection points are decreased by the continuous winding, the motor is decreased in cost. Further, a jumper wire connecting the coils is integrated at the inner diameter side of the coil, the outer diameter side of the coil is used as a free space, and the outer diameter side of the coil is connected to a motor housing so as to improve a cooling performance.